Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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ANTENNA WITH TWO ACTIVE RADIATORS
BACKGROUND OF THE INVENTION
L Field of the Invention
The present invention relates generally to antennas, and more
particularly, to a dual strip multiple frequency antenna. The invention
further relates to internal antennas for wireless devices, especially having
improved bandwidth and radiation characteristics.
IL Description of the Related Art
Antennas are an important component of wireless communication
devices and systems. Although antennas are available in numerous
different shapes and sizes, they each operate according to the same basic
electromagnetic principles. An antenna is a structure associated with a
region of transition between a guided wave and a free-space wave, or vice
versa. As a general principle, a guided wave traveling along a transmission
line which opens out will radiate as a free-space wave, also known as an
electromagnetic wave.
In recent years, with an increase in use of personal wireless
communication devices, such as hand-held and mobile cellular and
personal communication services (PCS) phones, the need for suitable small
antennas for such communication devices has increased. Recent
developments in integrated circuits and battery technology have enabled the
size and weight of such communication devices to be reduced drastically
over the past several years. One area in which a reduction in size is still
desired is communication device antennas. This is due to the fact that the
size of the antenna can play an important role in decreasing the size of the
device. In addition, the antenna size and shape impacts device aesthetics
and manufacturing costs.
One important factor to consider in designing antennas for wireless
communication devices is the antenna radiation pattern. In a typical
application, the communication device must be able to communicate with
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another such device or a base station, hub, or satellite which can be located
in any number of directions from the device. Consequently, it is essential
that the antennas for such wireless communication devices have an
approximately omnidirectional radiation pattern.
Another important factor to be considered in designing antennas for
wireless communication devices is the antenna's bandwidth. For example,
wireless devices such as phones used with PCS communication systems
operate over a frequency band of 1.85-1.99 GHz, thus, requiring a useful
bandwidth of 7.29 percent. A phone for use with typical cellular
communication systems operates over a frequency band of 824-894 MHz,
which requires a bandwidth of 8.14 percent. Accordingly, antennas for use
on these types of wireless communication devices must be designed to meet
the appropriate bandwidth requirements, or communication signals are
severely attenuated.
One type of antenna commonly used in wireless communication
devices is the whip antenna, which is easily retracted into the device when
not in use. There are, however, several disadvantages associated with the
whip antenna. Often, the whip antenna is subject to damage by catching on
objects, people, or surfaces when extended for use, or even when retracted.
Even when the whip antenna is designed to be retractable in order to
prevent such damage, it can extend across an entire dimension of the device
and interfere with placement of advanced features and circuits within some
portions of the device. It may also require a minimum device housing
dimension when retracted that is larger than desired. While the antenna
can be configured with additional telescoping sections to reduce size when
retracted, it would generally be perceived as less aesthetic, more flimsy or
unstable, or less operational by consumers.
Furthermore, a whip antenna has a radiation pattern that is toroidal
in nature, that is, shaped like a donut, with a null at the center. When a
cellular phone or other wireless device using such an antenna is held with
the antenna perpendicular to the ground, at a 90 degree angle to the ground
or local horizontal plane, this null has a central axis that is also inclined
at a
90 degree angle. This generally does not prevent reception of signals,
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because incoming signals are not constrained to arrive at a 90 degree angle
relative to the antenna. However, phone users frequently tilt their cellular
phones during use, causing any associated whip antenna to be tilted as well.
It has been observed that cellular phone users typically tilt their phones at
around a 60 degree angle relative to the local horizon (30 degrees from
vertical), causing the whip antenna to be inclined at a 60 degree angle. This
results in the null central axis also being oriented at a 60 degree angle. At
that angle, the null prevents reception of incoming signals arriving at a 60
degree angle. Unfortunately, incoming signals in cellular communication
systems often arrive at angles around or in the range of 60 degrees, and there
is an increasing likelihood that the mis-oriented null will prevent reception
of some signals.
Another type of antenna which might appear suitable for use in
wireless communication devices is a conformal antenna. Generally,
conformal antennas follow the shape of the surface on which they are
mounted and generally exhibit a very low profile. There are several
different types of conformal antennas, such as patch, microstrip, and
stripline antennas. Microstrip antennas, in particular, have recently been
used in personal communication devices.
As the term suggests, a microstrip antenna includes a patch or a
microstrip element, which is also commonly referred to as a radiator patch.
The length of the microstrip element is set in relation to the wavelength ~,o
associated with a resonant frequency fo, which is selected to match the
frequency of interest, such as 800 MHz or 1900 MHz. Commonly used
lengths of microstrip elements are half wavelength (7~/2) and quarter
wavelength (~/4). Although, a few types of microstrip antennas have
recently been used in wireless communication devices, further
improvement is desired in several areas. One such area in which a further
improvement is desired is a reduction in overall size. Another area i n
which significant improvement is required is in bandwidth. Current patch
or microstrip antenna designs do not appear to obtain the desired 7.29 to 8.14
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percent or more bandwidth characteristics desired for use in advanced
communication systems, in a practical size.
Therefore, a new antenna structure and technique for manufacturing
antennas are needed to achieve bandwidths more commensurate with
advanced communication system demands. In addition, the antenna
structure should be conducive to internal mounting to provide more
flexible component positioning within the wireless device, greatly improved
aesthetics, and decreased antenna damage.
SUMMARY OF THE INVENTION
The present invention is directed to a dual strip antenna. According
to the present invention, the dual strip antenna includes a first and a second
strip, each made of a conductive material, such as a metallic plate. The first
and second strips are separated by a dielectric material such as a dielectric
substrate or air. The first strip is electrically connected to the second
strip at
one end. In one embodiment of the present invention, the length of the
first strip is less than the length of the second strip and the surface area
of
the first strip is less than the surface area of the second strip.
A coaxial feed structure is connected or coupled to the dual strip
antenna. In a preferred embodiment, a positive terminal of the coaxial feed
is electrically connected to the first strip, and a negative terminal of the
coaxial feed is electrically connected to the second strip. In another
embodiment, these terminals or polarities are reversed.
In one embodiment of the present invention, the dual strip antenna
is constructed by forming, folding, or bending a flat conductive strip or
narrow sheet into a U-shaped structure, with each arm of the U forming one
of the strips. In other embodiments, other shapes are employed for the
transition, joint, or connection between the two strips. This includes,
quarter-circular, semi-circular, semi-elliptical, parabolic, angular, stepped,
as
well as both circular and squared C-, L-, and V-shaped transitions or folds.
The dual strip antenna can also be constructed by depositing one or
more layers of conductive material such as metallic compounds, conductive
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resins, or conductive ceramics in the form of strips on two sides of a
dielectric substrate. In this technique, one end of each of the strips is
electrically connected together. This electrical connection can be
implemented by a variety of means, such as conductive wires, solder
materials, conductive tapes, conductive compounds or one or more plated
through vias. The substrate provides a desired shape or relative positioning
for the strips deposited thereon.
In one embodiment of the present invention, the first and second
strips are positioned approximately parallel to one another, as in two
parallel planes. In another embodiment of the present invention, the first
and second strips flare out at the open end as they extend away from where
the first and second strips are electrically connected in order to provide
improved impedance matching 11, air or free space.
In further embodiments of the invention, the angle used for V
shaped structures can vary from less than 90 degrees to almost 180 degrees,
and curved structures can use relatively small or large radii, depending on
the mounting situation within the wireless device of interest. The width of
the conductors can be changed along their respective lengths such that they
taper, curve, or stepwise change to a narrow width toward an outer end.
Several of these features or shapes can be combined in a single antenna
structure.
In one further embodiment, the end of one of the strips is formed
with a transverse member so that it has a generally T-shaped end. This can
be implemented by attaching a transverse member to the end of one of the
strips. Alternatively, at least one of the strips is split or subdivided for a
short predetermined distance along its length. One of the subdivided
portions is folded or redirected at an angle to the strip, and the remaining
portion is redirected or folded at the negative of that angle with respect to
the strip. Typically, the angle is a 90 degree angle, although not required,
as
where a more Y-shaped end structure is acceptable.
For embodiments having folded elements, such as the T-shaped end,
those portions of a strip can be used as a support for mounting the
remainder of the antenna to a surface using bonding elements, a snap in
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channel, screw or other known fasteners, or fastening means. In this
configuration, the antenna elements are manufactured with sufficiently
thick material to prevent undue deformation of the antenna as needed.
This approach also provides a simple phone assembly technique by allowing
insertion of the antenna directly into the wireless device housing.
Furthermore, the shapes of the dual strip antenna strips can also vary
in a third dimension. A pair of strips that are formed as flat planar surfaces
in two dimensions can be curved along an arc, or folded in the third
direction. Simple offsets or short curves and folds in a third dimension are
also contemplated for some applications.
The dual strip antenna according to the present invention provides
an increase in bandwidth over typical quarter wavelength or half
wavelength patch antennas. Experimental results have shown that the dual
strip antenna has a bandwidth of at least approximately 10 percent, which is
very advantageous for use with wireless devices such as cellular and PCS
telephones.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention is described with reference to the
accompanying drawings, in which like reference numbers generally indicate
identical, functionally similar, and/or structurally similar elements, the
drawing in which an element first appears is indicated by the leftmost
digits) in the reference number, and wherein:
FIGS.1A and 1B illustrate a portable telephone having whip and
external helical antennas;
FIG. 2 illustrates a conventional microstrip patch antenna;
FIG. 3 illustrates a side view of the microstrip patch antenna of FIG. 2;
FIG.4 illustrates a dual strip antenna in accordance with one
embodiment of the present invention;
FIGS.5A-5I illustrate cross sectional views of several alternative
embodiments of the present invention using square transitions to connect
strips;
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FIGS.6A-6C illustrate cross sectional views of several other
alternative embodiments of the present invention using curved transitions
to connect strips;
FIGS.7A-7E illustrate cross sectional views of another several
alternative embodiments of the present invention using V-shaped
transitions to connect strips;
FIGS. 8A-8F illustrate cross sectional views of yet another several
alternative embodiments of the present invention using curved, angled,
and compound strip shapes;
FIGS.9A-9C illustrate perspective views of several other
embodiments of the present invention useful in certain other applications;
FIG.10 illustrates a measured frequency response of one embodiment
of the present invention suitable for use in cellular phones;
FIG.11 illustrates a measured frequency response of another
embodiment of the present invention suitable for use in PCS wireless
phones;
FIGS.12 and 13 illustrate measured field patterns for one embodiment
of the present invention;
FIGS.14A and 14B illustrate side and top views of one embodiment of
the present invention mounted within the phone of FIG.1; and
FIGS. 15A, 15B, 15C, and 15D illustrate alternative mechanisms for
mounting the antenna in place; and
FIGS.16A,16B, and 16C illustrate additional wireless devices in which
the present invention may be used.
DETAILED DESCRIPTION OF THE PREFERRED
EMBODIMENTS
I. Overview and Discussion of the Invention
While a conventional microstrip antenna possesses some
characteristics that make it suitable for use in personal communication
devices, further improvement in other areas of the microstrip antenna is
still desired in order to make it more desirable for use in wireless
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communication devices, such as cellular and PCS phones. One such area in
which further improvement is desired is in bandwidth. Generally, PCS and
cellular phones require approximately 8 percent bandwidth in order to
operate satisfactorily. Since the bandwidth of currently available microstrip
antennas falls approximately in the range of 1-2 percent, an increase in
bandwidth is desired in order to be more suitable for use in PCS and cellular
phones.
Another area in which further improvement is desired is the size of a
microstrip antenna. For example, a reduction in the size of a microstrip
antenna would make a wireless communication device in which it is used
more compact and aesthetic. In fact, this might even determine whether or
not such an antenna can be used in a wireless communication device at all.
In the past, a reduction in the size of a conventional microstrip antenna was
made possible by reducing the thickness of any dielectric substrate employed,
or increasing the dielectric constant. This, however, had the undesirable
effect of reducing the antenna bandwidth, thereby making it less suitable for
wireless communication devices.
Furthermore, the field pattern of conventional microstrip antennas,
such as patch radiators, is typically directional. Most patch radiators
radiate
only in an upper hemisphere relative to a local horizon for the antenna. As
stated earlier, this pattern moves or rotates with movement of the device
and can create undesirable nulls in coverage. Therefore, microstrip
antennas have not been very desirable for use in many wireless
communication devices.
The present invention provides a solution to the above and other
problems. The present invention is directed to a dual strip antenna that
operates as an open-ended parallel plate waveguide, but with asymmetrical
conductor terminations. The dual strip antenna provides increased
bandwidth and a reduction in size over other antenna designs while
retaining other characteristics that are desirable for use in wireless
communication devices.
The dual strip antenna according to the present invention can be built
near the top surface of a wireless or personal communication device such as
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a portable phone or may be mounted adjacent to or behind other elements
such as speakers, ear phones, I/O circuits, keypads, and so forth in the
wireless device. The dual strip antenna can also be built onto or into a
surface of a vehicle in which a wireless communication device may be used.
Unlike either a whip or external helical antenna, the dual strip
antenna of the present invention is not susceptible to damage by catching on
objects or surfaces. This antenna also does not consume interior space
needed for advanced features and circuits, nor require large housing
dimensions to accommodate when retracted. The dual strip antenna of the
present invention can be manufactured using automation and decreased
manual labor, which decreases costs and increases reliability. Furthermore,
the dual strip antenna radiates a nearly omnidirectional pattern, which
makes it suitable in many wireless communication devices.
II. Example Environment
Before describing the invention in detail, it is useful to describe an
exemplary environment in which the invention can be implemented. In a
broad sense, the invention can be implemented in any wireless device, such
as a personal communication device, wireless telephones, wireless modems,
facsimile devices, portable computers, pagers, message broadcast receivers,
and so forth. One such environment is a portable or handheld wireless
telephone, such as that used for cellular, PCS or other commercial
communication services. A variety of such wireless telephones, with
corresponding different housing shapes and styles, are known in the art.
FIGS.1A and 1B, illustrate a typical wireless telephone used i n
wireless communication systems, such as the cellular and PCS systems
discussed above. The wireless phone shown in FIG.1 (1A, 1B) has a more
traditional body shape or configuration, while other wireless phones, such
as shown in FIG.14, may have a "clam shell" or folding body configuration.
The telephone illustrated in FIG. 1 includes a whip antenna 104 and a
helical antenna 106, concentric with the whip, protruding from a housing
108. The front of the housing is shown supporting a speaker 110, a display
panel or screen 112, keypad 116, and a microphone or microphone access
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holes 118, which are typical wireless phone components, well known in the
art. In FIG.1A, antenna 104 is shown in an extended position typically
encountered during use, while in FIG.1B, antenna 104 is shown retracted.
This phone is used for purposes of illustration only, since there are a
variety
of wireless devices and phones, and associated physical configurations, in
which the present invention may be employed.
As discussed above, antenna 104 has several disadvantages. One, is
that it is subject to damage by catching on other items or surfaces when
extended during use, and sometimes even when retracted. Antenna 104
also consumes interior space of the phone in such a manner as to make
placement of components for advanced features and circuits, including
power sources such as batteries, more restrictive and less flexible. In
addition, antenna 104 may require minimum housing dimensions when
retracted that are unacceptably large. Antenna 106 also suffers from catching
on other items or surfaces during use, and cannot be retracted into phone
housing 102.
The present invention is described in terms of this example
environment. Description in these terms is provided for purposes of clarity
and convenience only. It is not intended that the invention be limited to
application in this example environment. After reading the following
description, it will become apparent to a person skilled in the relevant art
how to implement the invention in alternative environments. In fact, it
will be clear that the present invention can be utilized in any wireless
communications device, such as, but not limited to, a portable facsimile
machine or a portable computer with wireless communications capabilities,
and so forth, as discussed further below.
FIG. 2 shows a conventional microstrip patch antenna 200. Antenna
200 includes a microstrip element 204, a dielectric substrate 208, a ground
plane 212 and a feed point 216. Microstrip element 204 (also commonly
referred to as a radiator patch) and ground plane 212 are each made from a
layer of conductive material, such as a plate of copper.
The most commonly used microstrip element, and associated ground
plane, consists of a rectangular element, although microstrip elements and
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associated ground planes having other shapes, such as circular, are also used.
A microstrip element can be manufactured using a variety of known
techniques including being photo etched on one side of a printed circuit
board, while a ground plane is photo etched on the other side, or another
layer, of the printed circuit board. There are various other ways a microstrip
element and ground plane can be constructed, such as by selectively
depositing conductive material on a substrate, bonding plates to a dielectric,
or coating a plastic with a conductive material.
FIG. 3 shows a side view of conventional microstrip antenna 200. A
coaxial cable having a center conductor 220 and outer conductor 224 is
connected to antenna 200. Center conductor (positive terminal) 220 is
connected to microstrip element 204 at feed point 216. Outer connector
(negative terminal) 224 is connected to ground plane 212. The length L of
microstrip element 204 is generally equal to one-half wavelength (for the
frequency of interest) in dielectric substrate 208 (See chapter 7, page 7-2,
Antenna Engineering Handbook, Second Edition, Richard C. Johnson and
Henry Jasik), and is expressed by the following relationship:
L=O.S~,d =0.5~/ ~,
where L = length of microstrip element 204
c, = relative dielectric constant of dielectric substrate 208
~ = free space wavelength
~,d = wavelength in dielectric substrate 208
The variation in dielectric constant and feed inductance makes it hard
to predict exact dimensions, so a test element is usually built to determine
the exact length. The thickness t is usually much less than a wavelength,
usually on the order of 0.01 ~,o, to minimize or prevent transverse currents
or modes. The selected value of t is based on the bandwidth over which the
antenna must operate, and is discussed in greater detail later.
The width "w" of microstrip element 204 must be less than a
wavelength in the dielectric substrate material, that is, ~,d, so that higher-
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order modes will not be exited. An exception to this is where multiple
signal feeds are used to eliminate higher-order modes.
A second microstrip antenna commonly used is the quarter
wavelength microstrip antenna. The ground plane of the quarter
wavelength microstrip antenna generally has a much larger area than the
area of the microstrip element. The Iength of the microstrip element is
approximately a quarter wavelength at the frequency of interest in the
substrate material. The length of the ground plane is approximately one-
half wavelength at the frequency of interest in the substrate material. One
end of the microstrip element is electrically connected to the ground plane.
The bandwidth of a quarter wavelength microstrip antenna depends
on the thickness of the dielectric substrate. As stated before, PCS and
cellular
wireless phone operations require a bandwidth of approximately 8 percent.
In order for a quarter wavelength microstrip antenna to meet the 8 percent
bandwidth requirement, the thickness of dielectric substrate 208 must be
approximately 1.25 inches for the cellular frequency band (824 - 894 MHz)
and 0.5 inches for the PCS frequency band. This large of a thickness is
clearly
undesirable in a small wireless or personal communication device, where a
thickness of approximately 0.25 inches or less is desired. An antenna with a
larger thickness typically cannot be accommodated within the available
volume of most wireless communication devices.
III. The Present Invention
A dual strip antenna 400 which is constructed and operating according
to one embodiment of the present invention is shown in FIG. 4. In FIG. 4,
dual strip antenna 400 includes a first strip 404, a second strip 408, a
dielectric
substrate 412 and a coaxial feed 416. First strip 404 is electrically
connected to
second strip 408 at or adjacent to one end. The first and second strips are
each made of a conductive material such as, for example, copper, brass,
aluminum, silver or gold. First and second strips 404 and 408 are spaced
apart from each other by a dielectric material or substrate, such as air or a
foam known for such uses.
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In one embodiment of the present invention, first and second strips
404 and 408 are positioned substantially parallel to one another. In another
embodiment (see, for example, FIGS. 7A-7C and 9B), the first and second
strips flare out at an open end in order to provide better impedance
matching with air or free space.
The length of first strip' 404 primarily determines the resonant
frequency of dual strip antenna 400. In dual strip antenna 400, the length of
first strip 404 is sized appropriately for a particular operating frequency.
In a
conventional quarter wavelength microstrip antenna, the length of the
radiator patch is approximately ~,/4, where ~, is a wavelength at the
frequency
of interest of an electromagnetic wave in free space. In dual strip antenna
400, the length of first strip 404 is approximately 20 percent less than the
length of the radiator patch of a quarter wavelength microstrip antenna
operating at the same frequency. The length of second strip 408 is
approximately 40 percent less than the length of the ground plane of a
quarter wavelength microstrip antenna operating at the same frequency.
Thus, the present invention allows a significant reduction in the overall
length of the antenna, thereby making it more desirable for use in personal
communication devices.
Generally, the ground plane of a conventional microstrip antenna is
required to be much larger than the radiator patch. Typically, it is at least
one-half of the wavelength in dimension in order to work properly. In dual
strip antenna 400, the area of second strip 408 is much smaller than the area
of the ground plane of a conventional microstrip antenna, thereby
significantly reducing the overall size of the antenna.
A coaxial feed 416 is coupled to dual strip antenna 400. One terminal,
here the positive terminal or inner conductor, is electrically connected to
first strip 404. The other terminal, here the negative terminal or outer
conductor, is electrically connected to second strip 408. Coaxial feed 4I6
couples a signal unit (not shown), such as a transceiver or other known
wireless device or radio circuitry to dual strip antenna 400. Note that the
signal unit is used herein to refer to the functionality provided by a signal
source and/or signal receiver. Whether the signal unit provides one or both
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14
of these functions depends upon how antenna 400 is configured to operate
with the wireless device. Antenna 400 could, for example, be used or
operated solely as a transmission element, in which case the signal unit
operates as a signal source. Alternatively, the signal unit operates as a
signal
receiver when antenna 400 is used or operated solely as a reception element.
The signal unit provides both functions (as in a transceiver) when antenna
400 is connected or used as both transmission and receiver elements.
The dual strip antenna constructed according to the present invention
provides an increase in bandwidth over typical quarter wave-length or half
wave-length patch antennas. Experimental results have shown that the
dual strip antenna has a bandwidth of approximately 10 percent, which is
extremely desirable for wireless telephones. The increase in bandwidth is
made possible primarily by operating the dual strip antenna as an open-
ended parallel plate waveguide, but with asymmetrical conductor
terminations, rather than as a conventional microstrip patch antenna.
Unlike a conventional microstrip patch antenna having a radiator patch and
a ground plane, in the dual strip antenna, both the first and second strips
act
as active radiators. During operation of the dual strip antenna, surface
currents are induced in the first strip as well as in the second strip. The
operation of the dual strip antenna as an open-ended parallel plate
waveguide is made possible by selecting appropriate dimensions, that is,
length and width, for the first and second strips. In other words, the length
and the width of the first and second strips are carefully sized so that both
the first and second strips perform as active radiators. The inventor selected
appropriate dimensions of the first and second strips by using analytical
methods and EM simulation software that are well known in the art. The
simulation results were verified using known experimental methods.
In the present invention, the increase in bandwidth is achieved
without a corresponding increase in the size of the antenna. This is contrary
to the teachings of conventional patch antennas in which the bandwidth is
generally increased by increasing the thickness of the patch antennas,
thereby resulting in larger overall size for patch antennas. Thus, the present
invention allows the dual strip antenna to have a relatively small overall
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most applications and other angles can be employed, along with curved or
chamfered corners, as desired.
FIG. 5B shows that in order to accommodate a longer second strip,
that strip can be folded to maintain an overall desired length for the antenna
structure. FIG. 5C shows that the fold can be either toward or away from the
plane in which the first strip lays. FIG. 5D shows that the second strip can
be
folded back around, either partially or completely, the first strip. While
FIG. 5E shows the extension of the first strip through a folded architecture
as
well. FIG. 5F shows changes in direction for the first and second strips being
accomplished in smaller "steps".
FIGS. 5G and 5H, in particular, show embodiments wherein one of
the strips has either a T-shaped or Y-shaped end. In these configurations,
the T- or Y-shaped ends can be used as a support for mounting the rest of the
antenna to some surface using bonding elements, a snap in channel, screws
or other known fasteners. The T- or Y-shape can be formed by attaching
another strip 510 on the end of strip 508F or by splitting a portion of the
end
of strip 508F along a longitudinal axis, that is its length, and directing one
portion upward and the other downward, relative to the rest of the strip.
Alternatively, an end portion of each strip can be bent or directed at an
angle, as shown in FIG. 5I, to form the overall Y-shape. Here, the antenna
elements, including the T- or Y-shaped (angled) ends, may be constructed
with sufficiently thick material to support the weight of the entire antenna,
and maintain the desired spacing without deforming. This type of structure
provides a simple wireless device and antenna assembly technique.
Typically, the angle is a 90 degree angle, although not required, as where a
more Y-shaped end structure is acceptable
The cross sections of antenna embodiments shown in FIGS. 6A-6C
illustrate alternative shapes for the present invention using curved or
curvilinear transitions to connect the strips together. That is, in the
embodiments shown in FIGS.6A-6C, the first and second strips are
connected or joined together using a curved conductive connection element
or transition strip 606. Strip 606 can have a variety of shapes including, but
not limited to, quarter-circular, semi-circular, semi-elliptical, or
parabolic, or
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size and, thus, become more suitable for wireless communication devices,
such as PCS and cellular phones.
In one embodiment of the present invention, dual strip antenna 400
is constructed by bending a flat conductor sheet into a U-shape. A variety of
other shapes, such as, but not limited to, quarter-circular, semi-circular,
semi-elliptical, parabolic, angular, both circular and squared C-shaped, L-
shaped, and V-shaped can be used, depending on space and mounting
restrictions or requirements. The angle used at the joint for V-shaped
structures can vary from less than 90 degrees to almost 180 degrees. The
- 10 curved structures cam use relatively small or large radii.
The width of the conductors can be changed along their respective
lengths such that they taper, curve, or stepwise change to a narrower or
wider width toward the outer end (non-feed portion). As will be clearly
understood by those skilled in the art, several of these effects or shapes can
be combined in a single antenna structure. For example, an angled stepped
strip placed over a corresponding second strip which are both then curved or
folded in another dimension is possible.
Several cross-sectional views of alternative embodiments or shapes
for the strips of the present invention are shown in FIGS. 5A-5G, 6A-6C, 7A
7D and 8A-8F, where the last digit of the reference numerals indicates first
or
second strip, that is, 4 or 8, respectively. The first number and last
character
indicate the figure in which the element appears, as in 504A for FIG. 5A,
708B for FIG. 7B, and so forth.
The cross sections of antenna embodiments shown in FIGS. 5A-5I
illustrate alternative shapes for the present invention using rectangular or
square transitions to connect the strips together. That is, in the
embodiments shown in FIGS. 5A-5I, the first and second strips are connected
or joined together using a substantially straight conductive connection
element or transition strip 506 (506A-506I). In addition, further changes in
direction for the strips relative to each other are accomplished with
substantially square corners. Each change in direction involves positioning
a new portion of each strip substantially perpendicular, or at a 90 degree
angle, to a previous portion. Of course, these angles need not be precise for
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combinations of thereof. The curved structures can use relatively small or
large radii, as desired for a particular application. In addition, each of the
strips can be folded to maintain an overall desired length for the antenna
structure, as shown in FIGS. 5A-5I. FIG. 6A shows a generally semi-circular
curved transition, FIG. 6B shows a generally quarter-circular, or elliptical,
curved transition, and FIG. 6C shows a generally parabolic curved transition.
These types of transitions can also be used in combination.
The cross sections of antenna embodiments shown in FIGS.7A-7E
illustrate alternative shapes for the present invention using V-shaped
transitions to connect the strips together. That is, in the embodiments
shown in FIGS. 7A-7E, the first and second strips are connected or joined
together without using a separate conductive connection element or
transition strip, or by using a very small one. Instead, the first and second
strips extend from a common joint in an outward separation or flared
configuration. In addition, as before, each of the strips can be folded to
maintain an overall desired length for the antenna structure, as shown in
FIGS. 5A-5H.
FIGS. 7A and 7B, show a generally straight V-shaped or acute angular
transition where they join together. In FIG. 7B, the two strips bend again to
form generally parallel strips, or to provide a decreased angular slope with
respect to each other. In FIGS. 7C-7E, at least one of the two strips is
curved
after the initial V-shaped joint. In FIG. 7C, both strips are curved, such as
in
following an exponential or parabolic curve function. In FIG. 7D, only one
strip is curved, and in FIG. 7E, both strips are curved, but fold into
straight
sections. As before, these types of transitions can also be used in
combination, as desired, for a particular application.
FIGS. 8A-8F illustrate several alternative embodiments or shapes for
the strips of the present invention using curved, angled, and compound
strips. Here, the strips are positioned substantially parallel to each other
over their respective lengths, but follow circular, serpentine, or V-shaped
paths extending outward from where they are connected or joined together
using a conductive connection element or transition strip 806 (806A-806F).
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Furthermore, the shapes of the dual strip antenna can also vary in a
third dimension. A pair of strips that appear as flat planar surfaces in two
dimensions can be curved along an arc or be bent at an angle in a third
dimension (here z). Several embodiments of the present invention
wherein a pair of strips curve or bend in the z direction are shown in
FIGS. 9A-9C, where the last digit of the reference numerals indicates first or
second strip. These embodiments are very useful when the antenna is
desired to be placed within certain spaces in a wireless device which might
require the antenna to be "fit" around certain components or structures
within the device.
FIG. 9A shows the first and second strips as seen in FIG. 4 residing in
two planes that are substantially parallel to each other. However, each strip
is also curved in shape, along a third dimension, within each plane. FIG. 9B
shows the first and second strips as seen in FIG. 7A being connected together
in a V-shape or acute angular transition when viewed in two dimensions.
However, the two strips also have large angular displacements in a third
dimension, as well as the first strip tapering toward the open end. In
FIG. 9C, the two strips have a generally U-shaped transition where they join
together and form two generally parallel strips with respect to each other i n
two dimensions. However, both strips have a curved offset part way along
their respective lengths, as seen in a third dimension. '
Dual strip antenna 400 can also be constructed by etching or depositing
a metallic strip on two sides of a dielectric substrate and electrically
connecting the metallic strips together at one end by using one or more
plated through vias, jumpers, connectors, or wires. Dual strip antenna 400
can also be constructed by molding or forming a plastic material into a
support structure having a desired shape (U-, V-, or C-shaped, or curved,
rectangular, and so forth) and then plating or covering the plastic with
conductive material over appropriate portions using well known methods,
including conductive material in liquid form.
Dual snip antenna 400 provides a significantly broader bandwidth
than conventional microstrip antennas. As noted before, conventional
microstrip antennas have very narrow bandwidths, making them less
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19
desirable for use in personal communication devices, or even entirely
unusable. In contrast, dual strip antenna 400 provides approximately 10
percent bandwidth, thus, making it suitable for use in wireless
communication devices.
In the present invention, the increase in bandwidth is made possible
primarily by operating dual strip antenna 400 as an open-ended parallel plate
waveguide, but with asymmetrical conductor terminations. In contrast, the
bandwidth of conventional patch radiators is typically increased by
increasing the thickness of the dielectric substrate. However, increasing the
thickness increases the overall size of the patch radiator antenna making it
less desirable or even impractical for use in wireless communication
devices.
In dual strip antenna 400, both first and second strips 404 and 408
function as active radiators, i.e., an open-ended waveguide. This is made
possible by selecting appropriate dimensions, that is, the length and the
width, of first and second strips 404 and 408. In other words, the length and
the width of first and second strips are carefully sized so that both the
first
and second strips 404 and 408 perform as active radiators, at the wavelength
or frequency of interest.
In order to enhance the radiator or antenna bandwidth, the
dimensions of each strip, in a preferred embodiment, are chosen to establish
different center frequencies which are related to each other in a preselected
manner. For example, say that f a is the desired center frequency of the
antenna. The length of the shorter strip can be chosen such that its center
frequency resides at or around f o + 0 f , and the length of the longer strip
such that its center frequency is at or around f o - O f . This provides the
antenna with a wide bandwidth on the order of from 30 f / f o to 4O f / f o.
That
is, the use of the +/- frequency offset relative to f o results in a scheme
that
enhances the antenna radiator bandwidth. In this configuration, t1 f is
selected to be much smaller in magnitude than f a (D f « f o) so the resonant
frequency separation of the two strips is small. Its is believed that the
antenna will not perform satisfactorily if 0 f is chosen to be as large as f
o. In
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other words, this is not intended for use as a dual-band antenna with each
strip acting as an independent antenna radiator.
In one embodiment of the present invention, dual strip antenna 400
is sized appropriately for the cellular frequency band, that is, 824 - 894
MHz.
The dimensions of dual strip antenna 400 for the cellular frequency band are
given below in Table I.
Table I
length (L1) of first strip 404 3.0 inches
length (L2) of second strip 408 4.9 inches
width (Wl) of first strip 404 0.2 inches
width (W2) of second strip 408 0.4 inches
thickness (T) of dielectric substrate0.3 inches
412
In the above embodiment, 0.010 inch thick brass was used to construct
first and second strips 404 and 408, and air was used as dielectric substrate
412. The positive terminal of coaxial feed 416 was also connected to first
strip 404 at a distance of 0.3 inches from the closed end (shorted end) of the
antenna. Using material of such a thickness, or greater, allows the
mechanical structure of the antenna itself to support first strip 404 above
the
second strip 408. Otherwise, spacers or supports of non-conductive material
(or dielectric) are used to position the two strips relative to each other,
using
well known techniques.
The entire antenna or the strips can also be secured within portions of
the wireless device housing using posts, ridges, channels, or the like formed
in the material used to manufacture the housing. That is, such supports are
molded, or otherwise formed, in the wall of the device housing when
manufactured, such as by injection molding. These support elements can
then hold conductive strips in position when inserted between them, or
inside them, during assembly of the phone.
FIG.10 shows a measured frequency response of one embodiment of
dual strip antenna 400 sized to operate over the cellular frequency band.
FIG.10 shows that the antenna has a -7.94 dB frequency response at 825 MHz
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and a -9.22 dB frequency response at 960 MHz. Thus, the antenna has a 15.3
percent bandwidth.
In another embodiment of the present invention, dual strip antenna
400 is sized to operate over the PCS frequency band, that is, 1.85 - 1.99 GHz.
The dimensions of dual strip antenna 400 for the PCS frequency band is
given below in Table II.
Table II
length (Ll) of first strip 404 1.34 inches
length (L2) of second strip 408 2.21 inches
!
width (W1) of first strip 404 0.2 inches
width (W2) of second strip 408 0.2 inches
thickness (T) of dielectric substrate 0.08 inches
412
In the above embodiment, 0.010 inch thick brass was used to construct
first and second strips 404 and 408, and Rohacell foam (~. = 1.05) was used to
manufacture dielectric substrate 412. Also, the positive terminal of coaxial
feed 416 was connected to first strip 404 at a distance 0.2 inches from the
closed end (shorted end) of the antenna.
FIG.11 shows a measured frequency response of one embodiment of
dual strip antenna 400 sized to operate over the PCS frequency band. FIG.11
shows that the antenna has a -10 dB response at 1.85 GHz and at 1.99 GHz.
FIGS.12 and 13 show measured field patterns for one embodiment of
dual strip antenna 400 operating over the PCS frequency band. Specifically,
FIG.12 shows a plot of magnitude of the field energy in the azimuth plane,
while FIG.13 shows a plot of magnitude of the field energy in the elevation
plane. Both FIGS.12 and 13 show that the dual strip antenna has an
approximately omnidirectional radiation pattern, thereby making it suitable
for use in many wireless communication devices.
FIGS. 14A and 14B illustrate side and rear cutaway section views,
respectively, of one embodiment of the present invention mounted within
the phone of FIG.1. Such phones have various internal components
generally supported on one or more circuit broads for performing the
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various functions needed or desired. In FIGS. 14A and 14B, a circuit board
1402 is shown inside of housing 102 supporting various components such as
integrated circuits or chips 1404, discrete components 1406, such as resistors
and capacitors, and various connectors 1408. The panel display and
keyboard are typically mounted on the reverse side of board 1402, facing the
front of phone housing 102, with wires and connectors (not shown)
interfacing the speaker, microphone, or other similar elements to the
circuitry on board 1402.
In the side view of FIG.14A, circuit board 1402 is shown as comprising
multiple layers of conductive and dielectric materials, bonded together to
form what is referred to in the art as a multi-layer or printed circuit board
(PCB). Such boards are well known and understood in the art. This is
illustrated as dielectric material layer 1412 disposed next to metallic
conductor layer 1414 disposed next to dielectric material layer 1416
supporting or disposed next to metallic conductor layer 1418. Conductive
vias are used to interconnect various conductors on different layers or levels
with components on the outer surfaces Etched patterns on any given layer
determine interconnection patterns for that layer. In this configuration,
either layer 1414 or 1418 could form a ground layer or ground plane for
board 1402, as would be known in the art.
A dual strip antenna 1400 is shown mounted near an upper portion
of the housing adjacent to circuit board 1402. In FIGS. 14A and 14B, a ridge
1420 is shown adjacent to an upper strip, here strip one, of antenna 400,
while a ridge 1422 is shown adjacent to a lower strip of the antenna. In this
configuration ridge 1422 is also formed with an optional support lip or ledge
1424 for spacing the antenna from an adjacent housing wall. Both of the
ridges can employ such ledges, or not, as desired. Antenna 400 can simply be
secured between the ridges using a frictional or pressure fit, or by using one
of several known adhesives or bonding compounds known to be useful for
this function.
As discussed earlier, the antenna can be secured within portions of
the wireless device housing using posts, ridges, channels, or the like formed
in the material used to manufacture the housing. These support elements
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can then hold conductive strips in position when inserted between them, or
inside them, during assembly of the phone. Alternatively, antenna 1400 is
held in place using adhesives, or similar techniques to secure the antenna
against the side of the housing, preferably over an insulating material, or
against a bracket assembly which can be mounted in place using brackets,
screws, or similar fastening elements.
Some of these alternative mechanisms for mounting the antenna i n
place are illustrated in the views of FIGS.15A-15D. A series of bumps is
shown in 15A, the use of adhesives in 15B , the use of compounds in 15C.
A series of protrusions or bumps 1502 and 1504 are used in the
embodiment of FIG. 15A, to support the antenna much like ridges 1420 and
1422. These extensions can have circular, square, or other shapes as
appropriate for the desired application. In FIG. 15B, a set of channels 1506
are formed in a wall of housing 102, in which the antenna rests. Again,
adhesives, glues, potting compounds and the like can be used to secure the
antenna in place, as well as friction. In FIG. 15C, the antenna is simply
glued
or bonded in place against a surface, while in FIG. 15D, the antenna is
secured in place against a wall, support ridge, or even a bracket 1608, using
an adhesive layer or strip 1610 like element bonded to one of the strips
forming the antenna.
FIGS.16A,16B, and 16C illustrate additional wireless devices in which
the present invention may be used. An alternative style of wireless phone is
shown in FIGS.16A and 156, while a corner section of a housing for a
wireless device used in association with a computer, modem, or similar
portable electronic device is shown in FIG.16C.
In FIGS.16A and 16B, a phone 1600 is shown having a main housing
or body 1602 supporting a whip antenna 1604 and a helical antenna 16506.
As before, antenna 1604 is generally mounted to share a common central
axis with antenna 1606, so that it extends or protrudes through the center of
helical antenna 1606 when extended, although not required for proper
operation. These antennas are manufactured with lengths appropriate to
the frequency of interest or of use for the particular wireless device on
which
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24
they are used. Their specific design is well known and understood in the
relevant art.
The front of housing 1602 is also shown supporting a speaker 1610, a
display panel or screen 1612, a keypad 1614, and a microphone or
microphone opening 1616, and a connector 1618. In FIG.16B antenna 1604 is
in an extended position typically encountered during wireless device use,
while in FIG.16A antenna 1604 is shown retracted into housing 1602 (not
seen due to viewing angle).
In the cutaway view of FIG. 16C, antenna 400 is secured in place using
a combination of ridges 1420,1422, and extensions 1602 in an upper comer of
a wireless device 1630. Cable or conductor set 1632 is used to connect the
antenna to appropriate circuitry within the wireless device, such as a
portable computer, data terminal, facsimile machine, or the like.
While various embodiments of the present invention have been
described above, it should be understood that they have been presented by
way of example only, and not limitation. Thus, the breadth and scope of the
present invention should not be limited by any of the above-described
exemplary embodiments, but should be defined only in accordance with the
following claims and their equivalents.
What I claim as my invention is:
